Expensive word" (high CPC) isn't equal to "profitable word" (high earnings) due to the low volume of traffic expensive (niche) these words produce. The best way to find really profitable words is to rank keywords by cost/day (cost per click X clicks/day) rather than cost per click. You can Uncover thousands of These Profitable Keywords with Google Keyword Tool! Even words that pay pennies can bring in good money if you have the volume. Here is a Free list of the top 500 Most Profitable Words Get creative with these words and use this.
This is also my new and most favorable list of niche ( You can say keywords) Now build your blog along with these words and have a great time online